Disclosed herein are phase change inks containing amorphous and crystalline components, wherein the amorphous component is an oligomeric rosin-derived ester.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have also been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE 4205713AL, the disclosures of each of which are totally incorporated herein by reference.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, or the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, or the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
Known phase change inks generally contain components such as crystalline waxes and other materials that enable sharp and rapid phase transitions from the molten liquid state to the solid state. Many known phase change inks, however, exhibit disadvantages such as poor adhesion to coated paper substrates, resulting in poor scratch-resistance, poor image robustness, hard and brittle properties, poor ‘paper fold’ performance such as cracking and creasing of the image when the document is folded, and document offset. Further, the nonpolarity of these ink components often leads to compatibility issues with commonly available dyes and pigments, resulting in the need for more expensive or custom-designed colorants to ensure good solubility or dispersibility in the ink carrier and good long-term thermal stability to prevent colorant degradation or colorant migration.
Customers have also created a demand for materials that are bio-based, or derived at least partly from renewable resources. Energy and environmental policies, increasing and volatile oil prices, and public/political awareness of the rapid depletion of global fossil reserves has created a need to find sustainable monomers derived from biomaterials. By using bio-renewable feedstock, manufacturers can reduce their carbon footprint and move to a zero-carbon or even a carbon-neutral footprint. Bio-based polymers can also be very attractive in terms of specific energy and emission savings. Using bio-based feedstock can help provide new sources of income for domestic agriculture and reduce the economic risks and uncertainty associated with reliance on petroleum imported from unstable regions.
Accordingly, while known materials and processes are suitable for their intended purposes, there is a need for improved phase change inks. In addition, there is a need for phase change inks that exhibit sharp and rapid phase transitions from the molten liquid state to the solid state. Further, there is a need for phase change inks that exhibit good adhesion to coated paper substrates. Additionally, there is a need for phase change inks that exhibit good scratch-resistance. There is also a need for phase change inks that exhibit good image robustness. In addition, there is a need for phase change inks that exhibit good “paper fold” performance and reduced cracking and creasing of the image when the document is folded. Further, there is a need for phase change inks that exhibit good document offset performance. Additionally, there is a need for phase change inks that exhibit good compatibility with commonly available colorants. In addition, a need remains for phase change inks that contain at least some materials at least partly derived from renewable resources. Further, a need remains for phase change inks that can be prepared at desirably low cost. Additionally, a need remains for phase change inks that contain some biodegradable components.